This invention relates to electrochemical battery cells with strip-like electrodes and having a pressure contact between a lead from one of the electrodes and a side wall of the cell container.
Cells with adjacent positive and negative electrode strips can be used to provide good high rate discharge performance. Electrode assemblies containing such strips can include one or more pairs of flat, folded or spirally wound positive and negative electrodes. Cells can have housings including containers made from electrically conductive metals that are in electrical contact with one of the electrodes. In such cells the cell container can serve as or provide electrical contact to an external contact terminal.
Electrically conductive leads can be used for making electrical contact between electrodes and another cell component, such as the container or a cover closing a portion of the container. Leads can be in various forms and shapes, such as wires, strips and springs, and leads can be connected to containers or covers in various ways, including by fastening (e.g., welding) and by pressure.
Examples of cells in which an electrode lead is welded to an exposed edge or surface of an electrode current collector are found in U.S. Pat. No. 4,554,227, which is hereby incorporated by reference, and in unexamined Japanese patent publication numbers 05-121064 and 09-035739. In each of these the leads are electrically connected to external terminals by welding. In U.S. Pat. No. 4,554,227 the lead is bent to improve the strength of the welds to the exposed top edge of the electrode current collector.
Examples of cells in which pressure contact is used between a lead and an exposed portion of an electrode current collector at the core of the electrode assembly are found in U.S. Pat. Nos. 3,245,837 and 5,021,306, which are hereby incorporated by reference. In U.S. Pat. No. 3,245,837 the lead is an electrically conductive strip that is fastened to a cover plate and external terminal. In U.S. Pat. No. 5,021,306 the lead is a metal splint, and a leaf spring welded to the cap on the open end of the container makes pressure contact with the splint.
An example of a cell with leads that are bare portions of current collectors protruding from a plurality of electrodes is found in U.S. Patent Publication No. US 2002/0094478 A1, which is hereby incorporated by reference. The plurality of leads is bent and welded together, then fastened to a cell cover. The bends in the leads provide good weld strength.
An example of a cell with a lead extending from the bottom of an electrode assembly and welded to the bottom of the container is found in unexamined Japanese patent publication number 09-330697. A V-shaped groove is formed in a portion of the lead welded to the container to provide good weld strength.
Examples of cells with leads providing electrical contact between one electrode and the cell container and between the other electrode and a cover closing the container are found in U.S. Pat. Nos. 5,418,084 and 4,963,446, which are hereby incorporated by reference, as well as in FIGS. 1 and 2 herein. The cells are cylindrical cells with spirally wound electrode assemblies. As described in further detail below with reference to FIGS. 1 and 2, in each cell a spring provides electrical contact between the positive electrode and the cell cover, and a metal strip lead provides electrical contact between the negative electrode and the side wall of the container. The spring is fastened to the cell cover and makes pressure contact with the positive electrode current collector exposed at the top of the electrode assembly. The metal strip lead is fastened to the negative electrode and makes pressure contact with the inside surface of the container side wall. A reliable pressure contact is needed between the lead and the container under normal ranges of variability in manufacturing.
In a cell such as the cell in FIGS. 1 and 2, when made according to the prior art, the lead between the container side wall and the electrode assembly is held in pressure contact by a tight fit of the electrode assembly in the container. For reliable electrical contact, variability in the inside diameter of the container and the outside diameter of the electrode assembly must be small. One way of achieving a small variability in the electrode assembly outside diameter is to tightly control the thicknesses of the electrode strips. Another way is to vary the length of a strip of material that is wrapped around the external side surface of the electrode assembly to compensate for variations in thicknesses of the electrodes that can result in differences in diameter. This outer strip of material can be one or more strips of separator or a separate strip of overwrap material, as disclosed in U.S. Pat. No. 4,963,445, which is hereby incorporated by reference.
An object of the present invention is to provide reliable pressure contact between an electrode lead and the side wall of the cell container. Additional advantages of the invention can include, but are not limited to, improved contact reliability, increased tolerance of variability in manufacturing, reduced number of cell components, improved ease of manufacturing, reduced manufacturing scrap and reduced product cost.